Bush

ABSTRACT

Various embodiments provide a bush for isolating vibrations, the bush comprising: a first anchor part defining a longitudinal axis; a second anchor part disposed coaxially with respect to the first anchor part; a first resilient body operably engaged with the first anchor part; a second resilient body operably engaged with the second anchor part; and an inertial mass element disposed between the first anchor part and the second anchor part, wherein the inertial mass element is independently connected to the first resilient body and the second resilient body, wherein the first resilient body, second resilient body and inertial mass element are arrange to isolate vibrations between the first anchor part and the second anchor part within a predetermined operational frequency range, and wherein the inertial mass element is arranged to isolate the first anchor part and second anchor part from dynamic stiffness increases associated with eigenmodes of the inner resilient body and the outer resilient body in the predetermined operational frequency range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application of InternationalApplication No. PCT/EP2019/058691, filed Apr. 25, 2019, which claims thebenefit of British Application GB 1805838.8, filed on Apr. 9, 2018, bothof which are incorporated herein in their entireties.

FIELD OF THE INVENTION

The invention relates to a bush for resisting vibrations between twocomponents, such as the engine and chassis of a vehicle.

BACKGROUND TO THE INVENTION

Typically a bush for resisting vibration comprises two anchor parts thatare connected by resilient material, such as rubber. One anchor part isattached to one component of the vibrating machinery, and the otheranchor part attached to another component. As the two components vibraterelative to each other, the resilient material to provide isolationbetween vibrating component and anchor. Such bushes thus permit somerelative movement, but act to prevent excessive movement betweencomponents.

GB 2 364 558 discloses an example of a bush, in which the anchor partfor one component of the vibrating machinery is in the form of a hollowsleeve and the other anchor part in the form of a rod or tube extendingapproximately centrally and coaxially of the sleeve. A resilient body,e.g. of rubber or other suitable elastomeric material, is disposedwithin an annular volume between the sleeve and the rod. The resilientbody can be secured in place, e.g. by radial crimping of the sleevetowards the rod or by bonding via a vulcanisation process.

The resilient body between the sleeve and the rod represents a springelement for isolating vibration. The dynamic stiffness of this springelement varies with vibration frequency depending on a number offactors, including the resilient material used, and the shape andconfiguration of the connection between the sleeve and rod. However, inany given arrangement, the resilient body will exhibit one or moreeigenmodes where the dynamic stiffness increases and the vibrationalisolation between the interconnected components is reduced.

It is desirable for the eigenmodes of the resilient body to lie outsidea frequency range associated with normal operation of the components tobe interconnected (e.g. engine and chassis in a vehicle).

SUMMARY OF THE INVENTION

At its most general the present invention provides a bush having aninertial mass within a resilient interconnection between two anchorparts in order to provide a flat dynamic stiffness profile within apredetermined operational vibration frequency range. The predeterminedoperational vibration frequency range may be a sensitive vibrationfrequency range, e.g. associated with vibration frequency that may beexpected to occur regularly or for extending periods during operation.For example, where the bush is connected in a vehicle, the predeterminedoperational vibration frequency range may be associated with enginevibrations associated with cruising across a range of conventionalspeeds.

The anchor parts are interconnected by two independent spring elements(e.g. resilient bodies) which are separated by the inertial mass.Properties of the inertial mass and spring elements are selected toensure that any resonance conditions associated with either of thespring elements or the spring elements and inertial mass in combinationlie outside the predetermined operational vibration frequency range,e.g. in a non-sensitive operational vibration frequency range.

The bush may be used in many different applications or environments, forexample, the bush may be connected to an internal combustion engine, anelectric engine, a hybrid engine, a motor, an electric motor, a gearbox,a differential, or the like.

According to the invention, there is provided a bush for isolatingvibrations, the bush comprising: a first anchor part defining alongitudinal axis; a second anchor part disposed coaxially with respectto the first anchor part; a first resilient body operably engaged withthe first anchor part; a second resilient body operably engaged with thesecond anchor part; and an inertial mass element disposed between thefirst anchor part and the second anchor part, wherein the inertial masselement is independently connected to the first resilient body and thesecond resilient body, wherein the first resilient body, secondresilient body and inertial mass element are arrange to isolatevibrations between the first anchor part and the second anchor partwithin a predetermined operational frequency range, and wherein theinertial mass element has a mass selected to isolate the first anchorpart and second anchor part from dynamic stiffness increases associatedwith eigenmodes of the inner resilient body and the outer resilient bodyin the predetermined operational frequency range. In use, the bush maythus exhibit a flat or otherwise generally uniform dynamic stiffnessprofile across the predetermined operational frequency range.

The term “resilient” is used herein to indicate generally the ability torecoil or spring back after application of a deforming force.

Preferably the inertial mass element occupies a non-resonant conditionin the predetermined operational frequency range. In other words, therelative movement of the inertial mass element between the first anchorpart and second anchor part may lie within a range that is substantiallyuniform across the predetermined operational frequency range. Acombination of the inertial mass element and first and second resilientbodies may form a system that exhibits resonance. This resonance may becharacterised by an increase in the system's dynamic stiffness. Thisresonant condition (which may be viewed as an oscillation resonance ofthe inertial mass element) may be at a frequency below the predeterminedoperational frequency range, e.g. in a non-sensitive operationalfrequency range at or below 1000 Hz.

For example, if the bush is used in a vehicle, e.g. a vehicle with anelectric motor, a non-sensitive operational frequency range that isbelow a threshold of 1000 Hz can be a good area because electric motorstypically generate vibrations at this frequency at relatively lowspeeds. As such low speeds are not normally maintained for any length oftime, a driver would not perceive any noise in this non-sensitive range.In contrast, a high dynamic stiffness due to the resonant conditionoccurred at higher frequency range, there is a risk of it coincidingwith cruising of times spent at a certain speed for long periods oftime, which would be noticeable. It is to be understood that in anotherembodiment, a different threshold could be used, such as, for example,below 500 Hz or between 200 Hz and 800 Hz.

The bush may exhibit a dynamic stiffness characteristic having a singlepeak at a resonant frequency below the predetermined operationalfrequency range. The dynamic stiffness characteristic may include aplateau region across the predetermined operational frequency range. Theplateau region may be characterised by a variation in dynamic stiffnessof less than 1000 N/mm, preferably less than 500 N/mm.

The predetermined operational frequency range may be 500 to 2500 Hz orany sub-range thereof. The bush may be arranged to exhibit a low dynamicstiffness, e.g. less than 100 N/mm, within all or part of thepredetermined operational frequency range, e.g. within a range from 1000to 2000 Hz.

In one example, the first anchor part may be a rod extending along thelongitudinal axis. The second anchor part may comprise a sleevesurrounding the rod and defining an annular spacing therebetween. Inthis example, the inertial mass element may comprise a piece ofmaterial, such as a rigid tubular body, disposed in the annular spacing,e.g. coaxially with respect to the rod and the sleeve. The inertial masselement may be retained in this position by the first and secondresilient bodies. For example, the first resilient body may extendradially between an outer surface of the rod and an inner surface of theinertial mass element. The second resilient body may extend radiallybetween an outer surface of the inertial mass element and an innersurface of the sleeve.

The first resilient body may be a solid resilient member that fills anannular volume between the rod and the rigid tubular body.Alternatively, the first resilient body may be a moulded resilientmember having axially extending passages therethrough to facilitaterelative movement between the first and second anchor parts duringloading, for example, when the first and/or second anchor parts areloaded during operation.

The second resilient body may be a moulded resilient member havingaxially extending passages therethrough to facilitate relative movementbetween the first and second anchor parts during loading, for example,when the first and/or second anchor parts are loaded during operation.

The bush may include one or more snubber portions to physically limit anextent of relative radial movement between the first and second anchorparts. For instance, the first resilient body may include snubberportions formed within its axially extending passages to physicallylimit the extent of relative radial movement between the first andsecond anchor parts. Additionally or alternatively, the second resilientbody may include snubber portions formed within its axially extendingpassages to physically limit the extent of relative radial movementbetween the first and second anchor parts. Additionally oralternatively, at least one of the first and second anchor parts mayinclude a snubber portion which physically limits an extent of relativeradial movement between the first and second anchor parts. For example,the first anchor part may include a protrusion arranged to abut orimpact the second anchor part when a spacing (i.e. distance) between thefirst and second anchor parts falls below a predefined amount which isdefined by a shape/dimension (e.g. radial length) of the protrusion.Alternatively, the second anchor part may include the protrusion.Furthermore, the first anchor part may include a first protrusion andthe second anchor part may include a second protrusion, and the firstand second protrusions may be arranged to abut or impact each other whena spacing (i.e. distance) between the first and second anchor part fallsbelow a predefined amount which is defined by the combined dimensions(e.g. radial lengths) of the first and second protrusions.

In another example, the first anchor part may be a boss element and thesecond anchor part may be a cup element arranged to receive the bosselement therein. The boss element may be an elongate, e.g. rod-like,structure extending along the longitudinal axis of the bush. The cupelement may be a generally cylindrical structure that defines a cavitywithin which the boss element is receivable. In this example, the firstresilient body, second resilient body and inertial mass element maytogether form a frustoconical interconnection between the boss elementand the cup element. The inertial mass element may comprise a rigidseparating portion, e.g. in the form or a plate or the like, whichphysically separates the first resilient body from the second resilientbody. The rigid separating portion may be an annular planar elementextending circumferentially around the bush. A normal of the plane ofthe planar element may be inclined to the longitudinal axis.

The inertial mass element may comprise a snubber portion for limitingrelative axial movement between the boss element and the cup element.The snubber portion may comprise a radially extending surface, e.g.plate, that is arranged to abut either the cup element or boss elementif relative movement therebetween exceeds a threshold. For example, thecup element may comprise a top flange arranged to abut the snubberportion to restrict an axial distance by which the boss element ismovable into the cup element.

In use, the first anchor part may be connected to a first machinecomponent and the second anchor part may be connected to a secondmachine component, whereby the bush is operable to isolate vibrationsbetween the first machine component and second machine component. In anembodiment, both the first and second machine components may vibrate;however, in at least some other embodiments either the first or thesecond machine component may be fixed (i.e. cannot vibrate). The bushmay be configured for use in any suitable field. For example, the firstmachine component and second machine component are the engine andchassis of a vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are discussed in detail with reference tothe accompanying drawings, in which:

FIG. 1 is a perspective view of a bush that is an embodiment of thepresent invention;

FIGS. 2A and 2B show cross-sectional views of the bush of FIG. 1;

FIG. 3 is a graph showing dynamic stiffness against frequency for aknown bush and a bush that is an embodiment of the present invention;

FIG. 4 is a cross-sectional view of a known vertically mounted bush;

FIG. 5 is a cross-sectional view of a vertically mounted bush that isanother embodiment of the present invention;

FIG. 6 is a cross-sectional view of a vertically mounted bush that isanother embodiment of the present invention;

FIG. 7 is a perspective view of a bush that is a further embodiment ofthe present invention;

FIGS. 8A and 8B show cross-sectional views of the bush of FIG. 7;

FIG. 9 is a graph showing dynamic stiffness against frequency for thebush of FIG. 7;

FIG. 10A is a perspective view of a first end of a bush that is anotherfurther embodiment of the present invention;

FIG. 10B is a perspective view of a second end of the bush of FIG. 10A;

FIGS. 10C and 10D show cross-sectional views of the bush of FIG. 10A;

FIG. 11A is a perspective view of a first end of a bush that is yetanother further embodiment of the present invention;

FIG. 11B is a perspective view of a second end of the bush of FIG. 11A;and

FIGS. 11C and 11D show cross-sectional views of the bush of FIG. 11A.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bush 100 that is a first embodiment ofthe present invention. The bush 100 is a generally cylindrical structurethat defines a longitudinal axis. FIG. 2A shows a cross-section of thebush 100 perpendicular to the longitudinal axis. FIG. 2B shows across-section of the bush 100 parallel to the longitudinal axis.

The bush 100 comprises a series of components arranged coaxially aroundthe longitudinal axis. The components include a first anchor part 110that is surrounded by and operably engaged with an inner resilient body114. The inner resilient body 114 is surrounded by and operably engagedwith an inertial mass element 118. The inertial mass element 118 issurrounded by and operably engaged with an outer resilient body 116,which in turn is surrounded by and operably engaged with a second anchorpart 112. The function of each part will be described in more detailbelow. The bush 100 may have open end faces, as depicted in FIG. 1, orthe end faces of the bush 100 may be partially or entirely covered. Thebush may include fluid, e.g. hydraulic fluid, within voids defined inone or both of the resilient bodies.

The first anchor part 110 comprises a rigid rod, which may be a hollowtube, made from any suitable material, e.g. a metal such as steel. Thefirst anchor part 110 is configured to be attached to a first componentof vibrating machinery (not shown) in any conventional manner. In oneexample, the first anchor part 110 may have an inner diameter of 12 mmand an outer diameter of 25 mm, although the invention may be applicableto bushes having any dimensions.

The second anchor part 112 comprises a rigid sleeve, e.g. formed frommetal or the like, disposed coaxially with the first anchor part 110 todefine an annular space therebetween. The second anchor part 112 isconfigured to be attached to a second component of vibrating machinery(not shown). In one example, the second anchor part 112 may have aninner diameter of 105 mm and an outer diameter of 110 mm. The bush 100may thereby be used as a mounting device between two components. Forexample, the first component may be an engine or motor and the secondcomponent may be the chassis of a vehicle. The bush 100 may beparticularly suitable for use between the drive unit and chassis in anelectric vehicle.

Concentric with the first anchor part 110 and the second anchor part 112in the annular space therebetween, an inner resilient body 114 and anouter resilient body 116 are provided. The inner resilient body 114 andouter resilient body 116 may each be made of a resiliently deformablematerial such as rubber. The inner resilient body 114 and outerresilient body 116 may be formed from the same or different materials.In one example, the resilient material may be rubber having a hardnessof between 45 and 50 as measured with a Shore A durometer.

The inner resilient body 114 and outer resilient body 116 are separatedfrom each other by an inertial mass element 118, which in this exampleis a rigid annular element mounted between an outer surface of the innerresilient body 114 and an inner surface of the outer resilient body 116.

The inner resilient body 114, the inertial mass element 118, and theouter resilient body 116 may operate together to isolate vibrationsbetween the first anchor part 110 and the second anchor part 112. Inthis way, the first component may be isolated from vibrations of thesecond component, and vice versa, by interconnecting the two componentsusing the bush 100.

The inner resilient body 114 and the outer resilient body 116 mayoperate as independent springs on either side of the inertial masselement 118. The shape, material and configuration of the innerresilient body 114 may be selected so that the bush 100 exhibits adesirable dynamic stiffness characteristic, as discussed below. Theouter resilient body 116 may be configured as a movement limiter toprovide a level of control for significant relative movement eventsbetween the first and second anchor parts 110, 112, e.g. due toacceleration loads, pot hole events, cornering, crash, etc. Incombination, the outer resilient body 116 combined with the snubbers 120define a static stiffness curve which is tuned to give certain stiffnessfor a given force applied.

The inner resilient body 114 may comprise a solid rubber element fillingthe annular volume between the first anchor part 110 and the inertialmass element 118. The inner resilient body 114 may be directly mouldedbetween these two components.

In some examples, the inner resilient body 114 may be bonded to one orboth of the first anchor part 110 and the inertial mass element 118. Forexample, an inner bush formed by first anchor part 110 bonded to innerresilient body 114 may be push-fitted into inertial mass element 118 toincrease durability. Similarly it could be desirable to push fit thefirst anchor part 110 into a bush sub-assembly formed by the inertialmass element 118 bonded to the outer resilient body 116 to increasedurability. The increase in durability comes from pre-compressing therubber to remove residual stresses caused by the rubber shrinkingfollowing moulding.

One or both of the inner resilient body 114 and outer resilient body 116could either have voids/passageways or be solid rubber, as required bythe desired stiffness characteristic.

The outer resilient body 116 made have one or more axial passageways orvoids extending therethrough. In other words it need not completely fillthe annular volume between an outer surface of the inertial mass element118 and an inner surface of the second anchor part 112. The passagewaysor voids in the outer resilient body 116 may operate as buffers orsnubbers 120, 122 arranged to cushion large relative movements of thefirst component and/or the second component.

In this embodiment, the inertial mass element 118 is a rigid cylinder,e.g. made of a metal such as steel. The material and/or dimensions ofthe inertial mass element 118 may be selected in conjunction with thespring properties of the inner and outer resilient bodies 114, 116 sothat the inertial mass exhibits a resonance condition at a vibrationfrequency outside (e.g. below) the intended usage range of the bush.Under normal use of the bush, the inertial mass element 118 thusoccupies a non-resonant condition in which it isolates the dynamicstiffness increases associated with the eigenmodes of the inner andouter resilient bodies 114, 116. That is, each of the inner resilientbody 114 and outer resilient body 116 have independent resonantfrequencies, or eigenmodes, at which their dynamic stiffness increases.At vibration frequencies corresponding to these eigenmodes, theisolating effect provided by the inner resilient body 114 or the outerresilient body 166 is normal decreased. However, the presence ofinertial mass element 118 acts to reduce or remove these stiffnessincreases from the overall dynamic stiffness characteristic of the bush100 to provide a substantially flat dynamic stiffness characteristic forthe bush as a whole. The inertial mass element 118 therefore ensuresthat the bush 100 effectively isolates vibrations of a first componentof vibrating machinery from a second component of vibrating machineryacross an operating frequency range of each component.

In one non-limiting example, the inertial mass element may have a massof around 400 g. For example, the inner diameter of the inertial masselement 118 may be 55 mm and the outer diameter may be 65 mm.

FIG. 3 shows a graph of dynamic stiffness against frequency for a knownbush and a bush according to the present invention, such as bush 100shown in FIGS. 1 and 2A-2B.

As can been seen in FIG. 3, a dynamic stiffness characteristic 140 for aknown bush exhibit stiffness peaks 150, 152 corresponding to eigenmodesat approximately 1000 Hz and 2000 Hz. These peaks represent reducedvibrational isolation between two components interconnected by the bush.Where the bush is used to mount an engine or motor to the chassis of avehicle, in one example, this may result in an uncomfortable ride forpassengers. It is therefore desirable to reduce or eliminate thestiffness increases in the bush at these frequencies, and provide a bushhaving eigenmodes which lie outside a frequency range associated withnormal operation of interconnected components.

A bush such as that shown in FIGS. 1 and 2A-2B, may have a dynamicstiffness characteristic 142 that exhibits a single peak 154 at a lowerfrequency, e.g. less than 500 Hz. Preferably this peak occurs at afrequency below 400 Hz. This peak is the eigenmode, or resonance peak,of the inertial mass between the inner resilient body and the outerresilient body. Preferably this eigenmode is at a frequency below theoperating frequency range of the first component or the second componentwhich are interconnected by the bush. The resonant frequency of theinertial mass element is dependent on the mass of that element, and alsoon the size or material of the inner resilient body and the outerresilient body. By adjusting these parameters, the eigenmode of theinertial mass element may be ‘tuned’ to a desired frequency.

The presence of the inertial mass element in the bush reduces oreliminates increases dynamic stiffness above the resonant frequency ofthe inertial mass element itself. That is, there are no peaks in dynamicstiffness of the bush due to either the inner resilient body or theouter resilient body. Vibrations are therefore effectively isolated by abush according to the present invention across a broad range ofvibration frequencies. Preferably this broad range covers the operatingfrequency range of a first component and a second component to beinterconnected. For example, where a bush is used to interconnect anengine or motor and a chassis of a vehicle, use of a bush according tothe present invention ensures passenger comfort.

FIG. 4 shows a cross-sectional view of a known vertically mounted bush200. The bush 200 is generally cylindrical and comprises a first anchorpart 210 and a second anchor part 212. The first anchor part 210comprises a rigid boss element configured for attachment to a firstcomponent of vibrating machinery, and the second anchor part 212comprises a cup element for receiving the boss element. The secondanchor part 212 has an attachment region such as flange 213 configuredfor attachment to a second component of vibrating machinery. The secondanchor part 212 is concentric with, and spaced apart from, the firstanchor part 210 to define a generally annular region between the firstanchor part 210 and the second anchor part 212. A ring of resilientlydeformable material 214, such as rubber is disposed within this annularregion to connect the first anchor part 210 and the second anchor part212.

As the two components affixed to the bush 200 vibrate relative to eachother, the ring of resilient material 214 deforms to isolate thevibration. However, the resilient material 214 has one or moreeigenmodes at which the dynamic stiffness of the resilient material 214increases, reducing vibrational isolation between the interconnectedcomponents.

Relative movement between two interconnected components is limited inthe vertical (Z) direction, as viewed in FIG. 4, by an upper snubberplate 216 and a lower snubber plate 218.

The upper snubber plate 216 is connected to an upper end of the firstanchor part 210, and limits the range of movement of the first anchorpart 210 relative to the second anchor part 212 in a first direction(downwards as viewed in FIG. 4). The upper snubber plate 216 is sized toabut a snubbing surface 220 on the second anchor part 212 if relativemovement in the first direction exceeds a threshold.

The lower snubber plate 218 is connected to a bottom end of the firstanchor part 210, and limits the range of movement of the first anchorpart 210 relative to the second anchor part 212 in a second directionthat is opposite to the first direction (i.e. upwards as viewed in FIG.4). The lower snubber plate 218 is sized to abut an interior wall of thesecond anchor part 212 if relative movement between the first anchorpart 210 and second anchor part 212 in the second direction exceeds athreshold.

FIG. 5 shows a cross-sectional view of a vertically mounted bush 300that is another embodiment of the present invention.

Similarly to the embodiment discussed above with reference to FIGS. 1 to3, the anchor elements in bush 300 are connected to each other via afirst resilient body 314 and second resilient body 316 with an inertialmass element 318 disposed between the first resilient body 314 andsecond resilient body 316. In this example, the first resilient body 314is an annular element formed around, e.g. bonded to, a surface of thefirst anchor part 310. The first resilient body 314 may be bonded to aninclined surface of the first anchor part 310. The inclined surface maybe in the form of a frustocone. The second resilient body 316 may be anannular element formed on, e.g. bonded to, a surface of the secondanchor part 312. The second resilient body 316 may be bonded to aninclined surface of the second anchor part 312. The inclined surface maybe angled in a similar manner to the frustoconical surface of the firstanchor part 310, whereby the first resilient body 314 and secondresilient body 316 cooperate to bridge a gap between the first anchorpart 310 and second anchor part 312. The angled nature of the first andsecond resilient bodies may enable the bush to isolate vibrations havinga radial and axial components.

The inertial mass element 318 in this example comprises a rigid annularplate portion 320 that separates the first resilient body 314 from thesecond resilient body 316. The rigid annular plate portion may byinclined such that a normal to its plane lies at an acute angle to anaxis of the bush 300 and in line with a direction in which the firstresilient body 314 and second resilient body 316 bridge a gap betweenthe first anchor part 310 and second anchor part 312.

The inertial mass element 318 may also comprise a snubber portion 322for restricting the extent of relative axial movement between the firstanchor part 310 and second anchor part 312. In this example, the snubberportion is an annular flange that extends in a radial direction from anouter circumferential edge of the rigid annular plate portion away fromthe first and second resilient bodies. The second anchor part 312 mayhave a top flange 324 that extends in a radial direction. The annularflange may abut the top flange to restrict the distance by which thefirst anchor part 310 can move into the second anchor part 312.

In this example, the inertial mass element 318 may thus perform twofunctions. Firstly it can operate to reduce or remove dynamic stiffnessincreases in the bush 300 due to eigenmodes of the first resilient body314 and second resilient body 316, in a similar manner as the inertialmass element 118 of bush 100 described above with respect to FIGS. 1 to3. Secondly, it can operate to restrict relative axial movement betweenthe first and second anchor parts 310, 312 in a similar manner to theupper snubber part 216 discussed above with reference to FIG. 4.

FIG. 6 shows a cross-sectional view of a vertically mounted bush 400that is another embodiment of the present invention.

In this embodiment, a first anchor part 402 is connected to a vibratingelement (e.g. motor) and a second anchor part 404 is connected to achassis. The second anchor part 404 is a central rod member of ahydraulically damped vertical travel limiter. The second anchor part 404is secured within a housing 410 by a first resilient body 408, which isdisposed between the second anchor part 404 and rigid rings 412, 414that are fixed within the housing 410.

The housing 410 is secured to the first anchor part 402 by a secondresilient body 406, e.g. a rubber sleeve or the like.

The inertial mass element in this example comprises a combination of thecomponents of the hydraulically damped vertical travel limiter disposedbetween the first resilient body 408 and the second resilient body 406,i.e. the housing 410, rigid rings 412, 414 and hydraulic fluid 416within the housing 410. Thus, in additional to performing its normalfunction to limit vertical travel, the hydraulically damped device inFIG. 6 also provides an inertial mass to isolate the engine from thechassis

FIG. 7 is a perspective view of a bush 500 that is a further embodimentof the present invention. The bush 500 is a generally cylindricalstructure that defines a longitudinal axis. FIG. 8A shows across-section of the bush 500 perpendicular to the longitudinal axis.FIG. 8B shows a cross-section of the bush 500 parallel to thelongitudinal axis.

The bush 500 is a modified version of the bush 100 shown in FIG. 1.Therefore, in the following, a description of the bush 500 is providedwhich focusses on the aspects of bush 500 which differ from the bush 100of FIG. 1. Unless otherwise stated, it is to be understood that thestructure and operation of the bush 500 is the same as the structure andoperation of the bush 100 of FIG. 1.

The bush 500 has an inner resilient body 514 which includes one or moreaxial passageways or voids extending therethrough. In other words, thematerial of the inner resilient body 514 may not completely fill theannular volume between an inner surface of the inertial mass element 118and an outer surface of the first anchor part 110. The portions of theinner resilient body 514 circumferentially in-between the passagewaysmay be referred to as “legs”. The passageways facilitate relativemovement between the first and second anchor parts during loading.

The passageways in the inner resilient body 514 may include buffers orsnubbers 520 to physically limit the extent of relative radial movementbetween the first and second anchor parts. Specifically, the snubbers520 are arranged to restrict and cushion large relative movements (e.g.radial movements) of the first component (coupled to the first anchor110) and/or the second component (coupled to the second anchor 112). Forinstance, the snubbers 520 restrict and cushion movements so as toprotect the legs from becoming over-compressed and/or over-extended,which would otherwise reduce the lifespan of the bush 500. In theembodiment shown in FIG. 7, the snubbers 520 have a substantially “u” or“n” shaped cross section. Also, the passageways are substantially “u” or“n” in cross-section. However, it is to be understood that in some otherembodiments, the snubbers or passageways could have a different shapedcross-section.

In view of the above-described structure, the inner resilient body 514may be configured as a movement limiter to provide a level of controlfor significant relative movement (e.g. radial movement) events betweenthe first and second anchor parts 110, 112, e.g. due to accelerationloads, pot hole events, cornering, crash, etc. In combination, the innerresilient body 514 combined with the snubbers 520 define a staticstiffness curve which is tuned to give certain stiffness for a givenforce applied.

The inner resilient body 514 and the outer resilient body 116 mayoperate as independent springs. Since the inner and outer resilientbodies have corresponding structures, e.g. they both include passagewayswith snubber portions, the bush 500 is balanced and provides balancedvibration isolation because the inner and outer resilient bodies havesubstantially the same spring characteristics. For example, thepassageways with snubber portions mean that both the inner and outerresilient bodies (514, 116) have a relatively soft springcharacteristic, compared to the embodiment of FIG. 1 in which the outerresilient body 116 (with passages) is relatively soft but the innerresilient body 114 (without passages) is relatively hard.

It is to be understood that the spring characteristics of a resilientbody will depend on the number of passages and the number of snubberportions that the resilient body has. Therefore, in order that the bush500 remains balanced, the inner and outer resilient bodies may have thesame number of passageways and snubber portions. Also, the general shapeof the passages and snubber portions may be same in the inner resilientbody 514 and the outer resilient body 116, although the dimensions ofthe inner resilient body 514 will be less than those of the outerresilient body 116.

For example, under normal operating conditions, loading on the bush 500at the first and second anchor parts causes the passageways to distortto permit relative radial movement between the first and second anchorparts so as to isolate vibrations. Under these normal conditions, thedistortion of the passageways may be insufficient to cause the snubbers520 to physically limit the extent of relative radial movement betweenthe first and second anchors. For instance, the number of passagewaysand/or snubbers, and/or the dimensions/shape of the passageways and/orsnubbers may be chosen so that, under normal operating conditions, thepassageways distort without using the snubbers 520. However, underabnormal operating conditions, loading on the bush 500 at the first andsecond anchor parts causes the passageways to distort to such an extentthat the snubbers 520 physically limit the extent of relative radialmovement between the first and second anchor parts. Under these abnormalconditions, the snubbers 520 protect the resilient bodies fromover-compression and over-extension to prolong the operational life ofthe bush 500. Also, the snubbers 520 control a maximum displacement ofthe first and second anchor parts to reduce the chance that they (andthe components to which they are fixed) will hit neighbouring componentsand cause damage. For instance, the number of passageways and/orsnubbers, and/or the dimensions/shape of the passageways and/or snubbersmay be chosen so that, under abnormal operating conditions, thepassageways distort to such an extent that the snubbers 520 are used. Inan example, the bush 500 may be used in an electric vehicle (e.g. car),and the normal operating conditions may include maintaining a cruisingspeed (e.g. 50 km/h to 100 km/h) on a motorway. On the other hand, theabnormal operating conditions may include: accelerating the car from astationary start with maximum acceleration, performing an emergencystop, or driving over rough surfaces (e.g. pot holes, cobble stones).

FIG. 9 shows a graph of dynamic stiffness against frequency for the bush500 shown in FIGS. 7 and 8A-8B. The graph of FIG. 9 corresponds withthat of FIG. 3.

As seen on FIG. 9, the bush 500 may have a dynamic stiffnesscharacteristic 550 that exhibits a single peak 552 at a lower frequency,e.g. less than 500 Hz. Preferably this peak occurs at a frequency below400 Hz. This peak is the eigenmode, or resonance peak, of the inertialmass between the inner resilient body and the outer resilient body.Preferably this eigenmode is at a frequency below the operatingfrequency range of the first component or the second component which areinterconnected by the bush. The resonant frequency of the inertial masselement is dependent on the mass of that element, and also on the size,shape or material of the inner resilient body and the outer resilientbody. By adjusting these parameters, the eigenmode of the inertial masselement may be ‘tuned’ to a desired frequency.

The presence of the inertial mass element in the bush reduces oreliminates increases in dynamic stiffness above the resonant frequencyof the inertial mass element itself. That is, there are no peaks indynamic stiffness of the bush due to either the inner resilient body orthe outer resilient body. More specifically, the modifications to bush500, i.e. the introduction of passages with snubber portions 520 intothe inner resilient body 514 has improved the vibration isolationperformance, as can be seen by comparing the higher frequency portion ofdynamic stiffness characteristic 550 of FIG. 9 with the higher frequencyportion of dynamic stiffness characteristic 142 of FIG. 3. It is clearlyvisible that the characteristic 550 maintains a more consistent andreduced dynamic stiffness over higher frequencies compared to thecharacteristic 142. For example, see the region of characteristic 550highlighted by the reference sign 554.

In view of the above, vibrations are therefore effectively isolated bythe bush 500 across a broad range of vibration frequencies. Preferablythis broad range covers the operating frequency range of a firstcomponent and a second component to be interconnected. For example,where the bush 500 is used to interconnect an engine or motor and achassis of a vehicle, use of the bush 500 ensures passenger comfort.

FIG. 10A is a perspective view of a bush 600 that is a furtherembodiment of the present invention. The bush 600 is a generallycylindrical structure that defines a longitudinal axis. FIG. 10A shows afirst end of the bush 600, whereas FIG. 10B shows a second, opposite endof the bush 600. FIG. 10C shows a cross-section of the bush 600perpendicular to the longitudinal axis. FIG. 10D shows a cross-sectionof the bush 600 parallel to the longitudinal axis.

The bush 600 is a modified version of the bush 100 shown in FIG. 1.Therefore, in the following, a description of the bush 600 is providedwhich focusses on the aspects of bush 600 which differ from the bush 100of FIG. 1. Unless otherwise stated, it is to be understood that thestructure and operation of the bush 600 is the same as the structure andoperation of the bush 100 of FIG. 1.

The bush 600 has an inner resilient body 614 which includes one or moreaxial passageways or voids extending therethrough. In other words, thematerial of the inner resilient body 614 may not completely fill theannular volume between an inner surface of the inertial mass element 118and an outer surface of the first anchor part 110. The portions of theinner resilient body 614 circumferentially in-between the passagewaysmay be referred to as “legs”. The passageways facilitate relativemovement between the first and second anchor parts during loading.

The bush 600 has an outer resilient body 616 having a structure similarto that of the inner resilient body 614. That is, the outer resilientbody 616 has one or more axial passageways or voids extendingtherethrough.

In contrast to the bush 500, the passageways or voids of the bush 600may not include any buffers or snubbers. Instead, as seen moreparticularly on FIG. 10A and 10D, the second anchor part 112 includes asnubber portion 620 which is arranged to physically limit an extent ofrelative radial movement between the first anchor part 110 and thesecond anchor part 112. Specifically, the snubber portion 620 may beformed from a protrusion which extends radially towards the first anchorpart 110. The snubber portion 620 may have a substantially annular orring-shaped form, as seen most clearly on FIG. 10A. The protrusionextends only part way towards the first anchor part 110 so as to permitsome radial movement between the first and second anchor parts. That is,a radial length of the snubber 620 may be selected so as to permitradial movement up to a predetermined amount. As seen on FIG. 10D, a tipportion of the protrusion may be constructed from a different materialthan the rest of the snubber 620. For example, the tip portion may bemade from a resilient material (e.g. rubber) whereas the rest of thesnubber 620 may be made from a rigid material (e.g. metal).Alternatively, the whole snubber 620 may be made from a single material,such as a resilient material, like rubber.

In use, the snubber 620 is arranged to restrict and cushion largerelative movements (e.g. radial movements) of the first component(coupled to the first anchor 110) and/or the second component (coupledto the second anchor 112). For instance, the snubber 620 restricts andcushions movements so as to protect the legs of the first and secondresilient bodies from becoming over-compressed and/or over-extended,which would otherwise reduce the lifespan of the bush 600.

In view of the above-described structure, the snubber 620 is configuredas a movement limiter to provide a level of control for significantrelative movement (e.g. radial movement) events between the first andsecond anchor parts 110, 112, e.g. due to acceleration loads, pot holeevents, cornering, crash, etc. In combination, the snubber 620, theinner resilient body 614, and the outer resilient body 616 define astatic stiffness curve which is tuned to give certain stiffness for agiven force applied.

The inner resilient body 614 and the outer resilient body 616 mayoperate as independent springs. Since the inner and outer resilientbodies have corresponding structures, e.g. they both include passagewayswithout snubber portions, the bush 600 is balanced and provides balancedvibration isolation because the inner and outer resilient bodies havesubstantially the same spring characteristics.

It is to be understood that the spring characteristics of a resilientbody will depend on the number of passages that the resilient body has.Therefore, in order that the bush 600 remains balanced, the inner andouter resilient bodies may have the same number of passageways. Also,the general shape of the passages may be same in the inner resilientbody 614 and the outer resilient body 616, although the dimensions ofthe inner resilient body 614 will be less than those of the outerresilient body 616.

For example, under normal operating conditions, loading on the bush 600at the first and second anchor parts causes the passageways to distortto permit relative radial movement between the first and second anchorparts so as to isolate vibrations. Under these normal conditions, thedistortion of the passageways may be insufficient to cause the snubber620 to impact the first anchor part 110. As such, the snubber 620 doesnot physically limit the extent of relative radial movement between thefirst and second anchors. For instance, the number of passageways,and/or the dimensions/shape of the passageways and snubber 620 may bechosen so that, under normal operating conditions, the passagewaysdistort without using the snubber 620. However, under abnormal operatingconditions, loading on the bush 600 at the first and second anchor partscauses the passageways to distort to such an extent that the snubber 620physically limits the extent of relative radial movement between thefirst and second anchor parts (i.e. the snubber 620 hits the firstanchor 110). Under these abnormal conditions, the snubber 620 protectsthe resilient bodies from over-compression and over-extension to prolongthe operational life of the bush 600. Also, the snubber 620 controls amaximum displacement of the first and second anchor parts to reduce thechance that they (and the components to which they are fixed) will hitneighbouring components and cause damage. For instance, the number ofpassageways, and/or the dimensions/shape of the passageways and snubber620 may be chosen so that, under abnormal operating conditions, thepassageways distort to such an extent that the snubber 620 is used. Inan example, the bush 600 may be used in an electric vehicle (e.g. car),and the normal operating conditions may include maintaining a cruisingspeed (e.g. 50 km/h to 100 km/h) on a motorway. On the other hand, theabnormal operating conditions may include: accelerating the car from astationary start with maximum acceleration, performing an emergencystop, or driving over rough surfaces (e.g. pot holes, cobble stones).

An advantage of the snubber 620 compared to the snubbers 120 and 520, isthat the snubber 620 directly acts on the anchor parts because thesnubber 620 is directly attached to the second anchor part 112 anddirectly impacts the first anchor part 110. On the other hand, thesnubbers 120 and 520 are located in passages of the resilient bodies andso their snubbing effect is indirect because these snubbers do notattach to or impact the anchor parts directly. Also, the snubbers 120and 520 perform their snubbing effect through the inertial mass element118. Conversely, the snubbing effect of the snubber 620 is independentof the inertial mass element 118. Accordingly, when using the snubber620, the inertial mass element 118 has minimal or no major stiffnessrise (as in the embodiment of FIGS. 1, 2A and 2B) allowing the frequencypeak to remain stable under normal as well as abnormal operatingconditions.

FIG. 11A is a perspective view of a bush 700 that is a furtherembodiment of the present invention. The bush 700 is a generallycylindrical structure that defines a longitudinal axis. FIG. 11A shows afirst end of the bush 700, whereas FIG. 11B shows a second, opposite endof the bush 700. FIG. 11C shows a cross-section of the bush 700perpendicular to the longitudinal axis. FIG. 11D shows a cross-sectionof the bush 700 parallel to the longitudinal axis.

The bush 700 is a modified version of the bush 600 shown in FIGS. 10A-D.Therefore, in the following, a description of the bush 700 is providedwhich focusses on the aspects of bush 700 which differ from the bush 600of FIGS. 10A-D. Unless otherwise stated, it is to be understood that thestructure and operation of the bush 700 is the same as the structure andoperation of the bush 600 of FIGS. 10A-D.

As seen on FIGS. 11A and 11D, the first anchor part 110 includes asnubber portion 720 which is arranged to physically limit an extent ofrelative radial movement between the first anchor part 110 and thesecond anchor part 112. Specifically, the snubber portion 720 may beformed from a protrusion which extends radially towards the secondanchor part 112. The snubber portion 720 may have a substantiallyannular or ring-shaped form, as seen most clearly on FIG. 11A. Theprotrusion extends only part way towards the second anchor part 112 soas to permit some radial movement between the first and second anchorparts. That is, a radial length of the snubber 720 may be selected so asto permit radial movement up to a predetermined amount. As seen on FIG.11D, a tip portion of the protrusion may be constructed from a differentmaterial that the rest of the snubber 720. For example, the tip portionmay be made from a resilient material (e.g. rubber) whereas the rest ofthe snubber 720 may be made from a rigid material (e.g. metal).Alternatively, the whole snubber 720 may be made from a single material,such as a resilient material, like rubber.

In use, the snubber 720 is arranged to restrict and cushion largerelative movements (e.g. radial movements) of the first component(coupled to the first anchor 110) and/or the second component (coupledto the second anchor 112). For instance, the snubber 720 restricts andcushions movements so as to protect the legs of the first and secondresilient bodies from becoming over-compressed and/or over-extended,which would otherwise reduce the lifespan of the bush 700.

It is to be understood that in some other embodiments, the bush mayinclude both snubbers within passageways, as per FIGS. 2A or 8A, andsnubbers outside of passageways, as per FIGS. 10D or 11D.

Additionally, in some other embodiments, the bush may include both thesnubber 620 of FIG. 10D and the snubber 720 of FIG. 11D. Specifically,each snubber 620, 720 may extend towards each other but be dimensionedsuch that, under normal operating conditions, a gap or space ismaintained between the snubbers 620, 720. Then, under abnormal operatingconditions, the snubber 620 may impact the snubber 720 so as tophysically limit an extent of relative radial movement between the firstand second anchor parts. Of course, the snubbers 620, 720 may have thesame or different radial lengths.

Further, in some other embodiments, the snubber 620 or 720 may bepositioned at or near a middle of the bush. For instance, taking theexample of FIG. 11D, the snubber 620 may be attached to the first anchor110 half way along its length. Also, the inner resilient body 614, theinertial mass element 118, and the outer resilient body 616 may be splitinto two halves (e.g. via a cut perpendicular to a longitudinal axis ofthe first anchor 110) with the first half being positioned on the leftside of the snubber 620, and the second half being positioned on theright side of the snubber 620. A similar modification could be made tothe example of FIG. 10D.

1. A bush for isolating vibrations, the bush comprising: a first anchorpart defining a longitudinal axis; a second anchor part disposedcoaxially with respect to the first anchor part; a first resilient bodyoperably engaged with the first anchor part; a second resilient bodyoperably engaged with the second anchor part; and an inertial masselement disposed between the first anchor part and the second anchorpart, wherein the inertial mass element is independently connected tothe first resilient body and the second resilient body, wherein thefirst resilient body, second resilient body and inertial mass elementare arranged to isolate vibrations between the first anchor part and thesecond anchor part within a predetermined operational frequency range,wherein the inertial mass element is arranged to isolate the firstanchor part and second anchor part from dynamic stiffness increasesassociated with eigenmodes of the first resilient body and the secondresilient body in the predetermined operational frequency range, andwherein the bush includes one or more snubber portions to physicallylimit an extent of relative radial movement between the first and secondanchor parts, and wherein at least one of the first and second anchorparts includes the one or more snubber portions.
 2. A bush according toclaim 1, wherein the inertial mass element occupies a non-resonantcondition in the predetermined operational frequency range.
 3. A bushaccording to claim 1, wherein the inertial mass element occupies aresonant condition at a frequency below the predetermined operationalfrequency range.
 4. A bush according to claim 1 having a dynamicstiffness characteristic that exhibits a single peak at a resonantfrequency below the predetermined operational frequency range.
 5. A bushaccording to claim 4, wherein the resonant frequency is less than 1000Hz.
 6. A bush according to claim 1, wherein one of the first and secondresilient bodies includes axially extending passages therethrough tofacilitate relative movement between the first and second anchor partsduring loading.
 7. A bush according to claim 6, wherein both of thefirst and second resilient bodies include axially extending passagestherethrough to facilitate relative movement between the first andsecond anchor parts during loading.
 8. A bush according to claim 6,wherein the axially extending passages include the one or more snubberportions which physically limit an extent of relative radial movementbetween the first and second anchor parts.
 9. A bush according to claimI, wherein the first anchor part is a rod extending along thelongitudinal axis, and wherein the second anchor part is a sleevesurrounding the rod.
 10. A bush according to claim 9, wherein theinertial mass element is a rigid tubular body disposed coaxially withrespect to the rod in between the rod and the sleeve.
 11. A bushaccording to claim 10, wherein the first resilient body extends radiallybetween an outer surface of the rod and an inner surface of the rigidtubular body, and the second resilient body extends radially between anouter surface of the rigid tubular body and an inner surface of thesleeve.
 12. A bush according to claim 10, wherein the first resilientbody is a solid resilient member that fills an annular volume betweenthe rod and the rigid tubular body.
 13. A bush according to claim 1,wherein the first anchor part is a boss element and the second anchorpart is a cup element arranged to receive the boss element therein, andwherein the first resilient body, second resilient body and inertialmass element together form a frustoconical interconnection between theboss element and the cup element.
 14. A bush according to claim 13,wherein the inertial mass element comprises a snubber portion forlimiting relative axial movement between the boss element and the cupelement.
 15. A bush according to claim 14, wherein the snubber portioncomprises a radially extending plate.
 16. A bush according to claim 14,wherein the cup element comprises a top flange arranged to abut thesnubber portion to restrict an axial distance by which the boss elementis movable into the cup element.
 17. A bush according to claim 1,wherein the first anchor part is connectable to a first machinecomponent and the second anchor part is connectable to a second machinecomponent, whereby the bush is operable to isolate vibrations betweenthe first machine component and second machine component.
 18. A bushaccording to claim 17, wherein the first machine component and secondmachine component are the engine and chassis of a vehicle.